Sen. John McCain, R-Ariz., will sponsor a bill to strengthen campaign finance laws in this session of Congress despite vehement opposition to campaign finance reform from conservative Republican activists whose support he needs to win the party's nomination for president in 2008.

McCain recently had appeared to be backing away from his support of campaign finance reform, which has been a signature issue for him. But Friday, a top aide in his Senate office said that McCain will reintroduce a bill to further clamp down on independent "527" groups.

"Yes, it is McCain's bill and McCain will introduce it this Congress," Mark Salter, McCain's chief of staff, wrote in an e-mail. "Moreover, he wanted to introduce it earlier this month, but Senator (Russ) Feingold's staff suggested to our staff to wait a week or two."

Salter's response came after inquiries from the Politico about McCain's apparent retreat on campaign finance reform.

McCain and Feingold, a Wisconsin Democrat, together wrote the 2002 law that fundamentally over-hauled federal campaign finance regulations.

The measure earned the scorn of conservative Republicans and other political activists who argued that it stifled free speech rights by limiting political spending.

Last session, the two worked on a measure that would place tighter controls on the "527" groups that emerged to circumvent the limitations imposed by the McCain-Feingold measure.

This session, however, McCain has declined to support two other campaign finance measures that reformers consider priorities: one would expand the public financing system for presidential elections, and another would require grassroots organizations to disclose their funding and expenditures.

His lack of support for both worried campaign finance reformers who have considered him a champion of their cause.

McCain "has been supporting reform efforts for so long and has taken on the whole world when it comes to reform drives in Congress, so I'm convinced he truly believes in it," said Craig Holman, a lobbyist on campaign finance for Public Citizen.

"But it's very unfortunate that when it comes around to his presidential bid he's suddenly backing off, especially at such a critical moment. This is the year in which we're actually going to get some sweeping lobbying and ethics reform legislation, and he's not working with us on that," Holman said, adding that McCain's staff over the last few months had become unresponsive to entreaties to support campaign finance reforms.

McCain's campaign officials deny that he's backed away from supporting campaign finance reform. "He is a conservative candidate. He is going to run on reform should he decide to run," said Danny Diaz, a spokesman for McCain's exploratory campaign. "He's committed to reducing the amount of special interest money involved in politics. He has been. He will remain so."

However, in a survey recently posted on the exploratory campaign Web site, McCain officials asked supporters to comment on 25 specific proposals in four categories: taxes, government spending and regulation, the war in Iraq and the war on terror, and America's military. Campaign finance was not on the list.

Additionally, campaign officials have declined to quash speculation that he will opt out of the public financing system. And McCain voted last week to remove the grassroots lobbying disclosure provision that he previously supported. Many conservative activists, whose support McCain is courting, had opposed this measure.

McCain also has declined to sponsor a bill in the 110th Congress to expand the public financing system for presidential elections. The bill -- which will be introduced by Feingold -- is similar to one McCain sponsored in the 108th Congress, though he withheld his name on last session's measure.

By the time the bill was introduced last session, McCain was already considering a presidential run. Had he sponsored the bill, Diaz said, McCain might have faced charges of conflict of interest. It could have appeared as if he were trying to boost the public money that could be provided to campaigns, including his own.

Diaz described McCain's decision not to sponsor the bill as "a noble and pretty straightforward thing to do," and compared it to a judge recusing himself from a trial in which he or she has an interest. Public financing "is something that he still supports as a matter of policy," Diaz said, but he added that McCain "believes the public financing system is not fulfilling its original goal and must be reformed."

The leading contenders for the Democratic and Republican presidential nominations are expected to opt out of the public financing system, which provides taxpayer dollars to candidates who abide by restrictions on how much they can raise.

"A decision has not been made" about whether McCain will rely on public financing, Diaz said. As for the lobbying disclosure provision, which would have required grassroots organizations to disclose their financing, Diaz said McCain withdrew his support last year after meeting with groups across the political spectrum that argued the provision would have stymied citizen activism.

The leaders of six prominent campaign finance reform groups in Washington disagreed and urged the senators to support the provision, which the groups said would prevent abuses exposed in the Jack Abramoff lobbying scandal.

But one campaign finance reformer who has supported McCain's campaign finance efforts said his recent equivocation should be understood in the context of the campaign. The people whose support McCain needs don't count campaign finance as among their top issues, the reformer said, adding "some of the people hate McCain-Feingold and he's not going to run from it. I don't think he could, but he won't try to."

"There's going to be ongoing tension between his interest in campaign finance reform and the political reality that some of the people he's trying to reach are not interested in that issue."